The present invention relates generally to drive systems and more particularly to a method for reducing hard machining time of a constant velocity joints.
A key element in the driveline and drive train of a rear-wheel drive vehicle is a power transfer mechanism called a fixed axle. The fixed axle combines transmission and differential in a single unit. In rear-wheel drive systems used on vehicles, the drivetrain is compacted into an engine/transmission/propshaft/fixed-axle/driving-axle xe2x80x9cpackagexe2x80x9d that provides torque force to the rear wheels.
The main purpose of the driving axles is to transmit engine torque from the final drive unit to the rear wheels. As part of the driving axle assembly, the constant velocity joints (xe2x80x9cCV jointsxe2x80x9d) are designed to operate at various angles to accommodate up and down movement of the rear wheels. Some CV joints also permit shaft length changes caused by up-and-down movement of the rear wheels and by fixed axle movement due to torque reaction.
The driving axle typically has CV joints at both xe2x80x9cinboardxe2x80x9d and xe2x80x9coutboardxe2x80x9d ends. The inboard CV joint generally consists of an outer race and stub shaft, an inner race, a cage, ball bearings, and a ball retainer. The outer race is called a xe2x80x9cplungexe2x80x9d type because it has elongated grooves which allows the bearing cage and bearings to slide in and out as the front wheels go up and down. The inboard CV joint stub shaft is splined to the differential side gear.
The outboard CV joint generally consists of an outer race, a cage, an inner race, and ball bearings. The CV joint outer race stub shaft is splined to accommodate a splined hub that is pressed on and held by a staked nut. Typically, this is referred to as a ball-type fixed CV joint.
These CV joints use the rolling ball bearings in curved grooves to obtain uniform motion. The balls, which are the driving contact, move laterally as the joint rotates. This permits the point of driving contact between the two halves of the coupling to remain in a plane that bisects the angle between the two shafts.
Typically, fixed, ball-type CV joints are manufactured by heat treating the near net-shaped cage and ball track to a desired surface hardness and case depth. The surfaces are then hard machined the entire length of the bearing surfaces to provide a minimum of 45 degrees of articulation.
One problem with the currently available manufacturing technology is that amount of time necessary to hard machine the entire surface of the ball track and/or cage track area. This also has an adverse effect on tool life. In a rear wheel drive application, forty-five degrees of articulation is not required since the outboard CV joint does not have to compensate for wheel steering as in the front wheels. The fixed ball type CV joint can be optimized to operate at reduced angles by minimizing the functional ball track and cage track areas. Thus, only a portion of the ball track and cage track areas, in low angle operations, needs to be hard machined.
Objects of the present invention are to reduce the amount of hard machining time for the ball track and/or cage track areas and to improve the tool life by minimizing the functional ball track and/or cage track area that must be hard machined after heat treating.
The above objects are accomplished by forming a recess in the ball track and/or cage track areas that are non-functional during low angle operation of the CV joint assembly. This is done prior to heat treat hardening of the component either during the forging process or during machining of the unhardened component.
This new process results in a significant reduction in the hard machining area of the ball and cage track surfaces. The cage and ball track relief areas have a larger formed (prior to heat treat) radius than the finished radius, providing hard machining tool clearance. This reduction in hard machining area also improves the tool life by reducing the amount of hard machining that is done by the tool per unit.